Scientific Method —

Disorienting mosquitoes with a blend of odors

A combination of odorous chemicals can potentially disorient mosquitoes, …

As we enjoy the outdoors through various summer activities, we also have to deal with pests like mosquitoes, which are potential disease carriers, on top of being annoying. DEET (N,N-diethyl-m-toluamide) is an effective repellent, but it requires high concentrations, can be a skin irritant, and is damaging to some materials, including plastics. Certain species of mosquitoes are also developing resistance to DEET. There is a real need for new repellents, particularly in developing countries that are vulnerable to malaria and dengue.

To further this search, scientists are looking for ways to disrupt the ability of female mosquitoes to detect carbon dioxide (CO2), a gas that we exhale. Female mosquitoes use carbon dioxide as a cue for finding hosts. Once they detect a plume of the gas, they will fly upwind to find the source. In a recent issue of Nature, a paper by Stephanie Turner and her colleagues reports that a combination of odors could disrupt the mosquito’s response to carbon dioxide.

The researchers screened for chemicals that would affect behavioral response to carbon dioxide in female mosquitoes from three major disease-transmitting species: Anopheles gambiae, Culex quinquefasciatus, and A. aegypti. Turner found that 2,3-butanedione (a natural byproduct of fermentation that has a buttery flavor) activated the cpA neuron, which is a highly sensitive carbon dioxide detector. A brief exposure (a one-second pulse) causes the neurons to be significantly less sensitive to carbon dioxide for at least 5.5 minutes.

To further enhance the effect of 2,3-butanedione, the authors tested multiple combinations of chemical odors. They found that a combination of 2,3-butanedione, 1-hexanol (a volatile organic alcohol), 1-butanal (an acrid-smelling flammable liquid), and 1-pentanal (a food additive that has a woody, nutty, and fruity odor) was the most effective at making mosquitoes unresponsive to carbon dioxide.

Turner and her team tested this combination of four chemicals in semi-field experiments in Kenya. They placed two huts in a large enclosed greenhouse and equipped the huts with carbon dioxide traps for mosquitoes. Then the researchers dispensed the odor blend (one percent in paraffin oil) using small fans in one of the huts. In overnight experiments, Turner and her team released female mosquitoes (Culex quinquefasciatus) in the greenhouse and counted the number of mosquitoes entering the huts and traps.

They found that the odor blend treatment significantly reduced the number of mosquitoes entering the huts and flying into the carbon dioxide traps (about 40 percent in the untreated hut compared to roughly 20 percent in the treated hut).

In a separate corroborating experiment, Turner and her colleagues placed only one hut in a greenhouse. When the hut was treated with the odor blend (three percent in paraffin oil), only about 10 percent of the mosquitoes entered the hut and reached the carbon dioxide trap, while roughly 35 percent of the mosquitoes would reach the trap in the hut when there is no treatment.

The blend of the four odorous chemicals appears to disorient the mosquitoes, disrupting their ability to seek out carbon dioxide and fly towards the source. Dispensing a blend of odorous repellents has the benefit of being able to protect many people in a given area. You also wouldn’t need to apply this blend directly on your skin, but you would end up breathing it in.

Turner and her team also found that the odor blend does not diminish the effect of DEET on mosquitoes. Thus, the blend could potentially be used in conjunction with DEET. You would then have both short-range repellency from DEET and long-range repellency from the odor blend. However, the authors have not reported the maximum range of operation for a given amount of the chemical mixture.

One caveat is that the odorous chemicals are not safe for use around humans without further testing, as they could be problematic in high concentrations. However, the researchers have proved that the concept of using disorienting odors works for repelling mosquitoes. As with many drugs, the chemical structure of the odors could be modified so that they are still effective without being harmful to humans.

Yun Xie
Yun Xie / Yun Xie is a contributing science writer at Ars, where she covers the latest advancements in science and technology for Ars. She currently works in scientific communications, policy, and review. Emailreenxie@gmail.com//Twitter@yun_xie

23 Reader Comments

Obviously this will not work in all cases, but one of the best ways to fight misquotes without any chemicals at all is to situate some oscillating fans in your vicinity(like on a patio or deck). Misquotes are relatively weak flyers and the fans will simply push them away.

Obviously this will not work in all cases, but one of the best ways to fight misquotes without any chemicals at all is to situate some oscillating fans in your vicinity(like on a patio or deck). Misquotes are relatively weak flyers and the fans will simply push them away.

im actually kinda curious if they took that into account, since they used small fans to circulate the odor.

Quote:

Then the researchers dispensed the odor blend (one percent in paraffin oil) using small fans in one of the huts.

Reminds me of old crack buddies- er cracker buddies in FL swamps building 'houses' that sell in the dry months to damyankees(they move south and stay), this guy from uneevarsity asked about the skeeter problem. And my good ole boy replies we're up to our arses in snakes and gators and you're worried about the skeeter problem?

And to this day more people die from skeeters than the snakes and gators. Pets on the other hand...

Avon(calling) used to make a sunscreen... and the scent was 100 percent effective with ALL bugcritters(except Critter- hes mostly human and family and technically not a bug anymore).

Okay with sun too. Then they released a new and improved bug repellant. Which burned some(aleergic reaction) and seemed to attract anything that flew. Or crawled- down critter!

Also in dependent research(I practice on my kids) found that if a smell truly obnoxious you dont care about the bugs.

Gee I miss Florida and going to school and then work. But I became a teenager and left school behind and had to work two jobs like everyone else Not retired from a good union job.

Obviously this will not work in all cases, but one of the best ways to fight misquotes without any chemicals at all is to situate some oscillating fans in your vicinity(like on a patio or deck). Misquotes are relatively weak flyers and the fans will simply push them away.

That can work with some bloodsuckers, but some bloodsucker types or swarms can defeat the fan strategy. I am receptive to any science that keeps those tiny vampires away from my life nectar.

Reminds me of old crack buddies- er cracker buddies in FL swamps building 'houses' that sell in the dry months to damyankees(they move south and stay), this guy from uneevarsity asked about the skeeter problem. And my good ole boy replies we're up to our arses in snakes and gators and you're worried about the skeeter problem?

And to this day more people die from skeeters than the snakes and gators. Pets on the other hand...

Avon(calling) used to make a sunscreen... and the scent was 100 percent effective with ALL bugcritters(except Critter- hes mostly human and family and technically not a bug anymore).

Okay with sun too. Then they released a new and improved bug repellant. Which burned some(aleergic reaction) and seemed to attract anything that flew. Or crawled- down critter!

Also in dependent research(I practice on my kids) found that if a smell truly obnoxious you dont care about the bugs.

Gee I miss Florida and going to school and then work. But I became a teenager and left school behind and had to work two jobs like everyone else Not retired from a good union job.

Missing DDT. But that is a different set of bugs.

I just finished perusing a couple weeks' worth of this guy's comments. Is insanity contagious?

This is a fairly useless article, as it talks about one test done by one set of researchers that produced a mildly effective way of keeping mosquitoes away.I guess I learned that mosquitoes don't like some weird stinky mixture that some scientist developed, that isn't and probably won't be available for years, if ever.I think I'm just bitchy because I was really hoping for a realistic, immediate solution to mosquitoes when I saw the headline. For now, I'll just keep going with the DEET.

Hey hey hey. Please don't scare away wishful thought about someday ending the bloodsucker scurge. I fully support any person willing to endure swamps to find a way to get rid of mosquitoes. I hate those damn things. Flies are a close second.

Reminds me of old crack buddies- er cracker buddies in FL swamps building 'houses' that sell in the dry months to damyankees(they move south and stay), this guy from uneevarsity asked about the skeeter problem. And my good ole boy replies we're up to our arses in snakes and gators and you're worried about the skeeter problem?And to this day more people die from skeeters than the snakes and gators. Pets on the other hand...Avon(calling) used to make a sunscreen... and the scent was 100 percent effective with ALL bugcritters(except Critter- hes mostly human and family and technically not a bug anymore).Okay with sun too. Then they released a new and improved bug repellant. Which burned some(aleergic reaction) and seemed to attract anything that flew. Or crawled- down critter!Also in dependent research(I practice on my kids) found that if a smell truly obnoxious you dont care about the bugs.Gee I miss Florida and going to school and then work. But I became a teenager and left school behind and had to work two jobs like everyone else Not retired from a good union job.Missing DDT. But that is a different set of bugs.

I just finished perusing a couple weeks' worth of this guy's comments. Is insanity contagious?

This guy's insanity is. Walk...no run to your nearest psychiatrist for immediate medication.

Wow, I discovered this 25 years ago experimenting with various smells. I would have assumed it was already established science. If anyone is wondering garlic was the most effective followed by Avon.

No one would even care about this if they hadn't erroneously banned DDT which now sits on the same list as the cell phone (could possibly maybe in huge concentrations cause cancer we really don't know), way to go World Health Organization.

Wow, I discovered this 25 years ago experimenting with various smells. I would have assumed it was already established science. If anyone is wondering garlic was the most effective followed by Avon.

Garlic always works well on vampires.

Where I live, we have loads of mosquitoes. I generally use DEET based repellents because they work very well. There's other products, like these little coil things you burn, as well as electronic devices that you can wear around your neck on a lanyard, but I'm not sure if those are legit. At any rate, I've found when I'm out camping, throwing some wet birch tree leaves on the fire creates a smoke and odor that seems to keep the mosquitoes away.

I remember reading about some work on genetically modifying female mosquitoes that then would be released into a population of mosquitoes. Her offspring would then be infertile and would use up many of the resources of the population and cause population decline. I'm sure there are massive concerns with releasing breeding-capable GMOs into the wild, but the idea is pretty interesting and could actually do something about the problem without any chemicals.

Mosquitos love me. There could be ten people in the room and 90% of them come to me. This particular product works really well for me and the smell is reasonably pleasant (kind of a lemon spice). I don't have any business relationship with the company.

There was an article somewhere I read recently about grapefruit extracts being really good at actually killing mosquitos, but this is still in research stage.

Does this not sound like a great beer? Buttery, woody/nutty/fruity, and volatile organic alcohol that causes less sensitivity in one second pulses.. AND it lets one avoid mosquitos? I'll take a keg of the stuff.

Quote:

Anopheles gambiae, Culex quinquefasciatus, and A. aegypti. Turner found that 2,3-butanedione (a natural byproduct of fermentation that has a buttery flavor) activated the cpA neuron, which is a highly sensitive carbon dioxide detector. A brief exposure (a one-second pulse) causes the neurons to be significantly less sensitive to carbon dioxide for at least 5.5 minutes.

To further enhance the effect of 2,3-butanedione, the authors tested multiple combinations of chemical odors. They found that a combination of 2,3-butanedione, 1-hexanol (a volatile organic alcohol), 1-butanal (an acrid-smelling flammable liquid), and 1-pentanal (a food additive that has a woody, nutty, and fruity odor) was the most effective at making mosquitoes unresponsive to carbon dioxide.

I had a band in San Francisco, and we rented space in a rehearsal studio half a block from the sewage treatment plant at the end of the street. Mosquitoes are rare in SF, but there were some in this area since there was plenty of standing water just down the street.

One day I said something about the mosquitoes and someone said, "oh, that's from Mark's drum riser." I asked what the hell he were talking about, and he explained that "some mosquitoes laid their eggs on Mark's drum riser and they hatched when he brought it into our rehearsal room." I explained that mosquitoes ONLY lay their eggs on water, and that, being a native of Florida, it was a well known fact because they often warned on TV about leaving anything that could collect water, like flower pots, tires, old cans, etc. They nodded and I figured that was the end of it.

About a month later, someone said something about mosquitoes, and someone else said, "oh, that's from Mark's drum riser." So much for trying to acquaint these guys with basic facts . . .

Does this not sound like a great beer? Buttery, woody/nutty/fruity, and volatile organic alcohol that causes less sensitivity in one second pulses.. AND it lets one avoid mosquitos? I'll take a keg of the stuff.

Quote:

Anopheles gambiae, Culex quinquefasciatus, and A. aegypti. Turner found that 2,3-butanedione (a natural byproduct of fermentation that has a buttery flavor) activated the cpA neuron, which is a highly sensitive carbon dioxide detector. A brief exposure (a one-second pulse) causes the neurons to be significantly less sensitive to carbon dioxide for at least 5.5 minutes.

To further enhance the effect of 2,3-butanedione, the authors tested multiple combinations of chemical odors. They found that a combination of 2,3-butanedione, 1-hexanol (a volatile organic alcohol), 1-butanal (an acrid-smelling flammable liquid), and 1-pentanal (a food additive that has a woody, nutty, and fruity odor) was the most effective at making mosquitoes unresponsive to carbon dioxide.

Diacetyl is normally not a desirable item to have in your beer. Trust me. I had to watch 5 gallons go down the drain one time because I didn't keep a better eye on the ol' yeasties.

Hi. Let me introduce myself. SuperMosquitoMagnet. It wouldn't be so bad if A) I did not have a rather violent histaminic reaction to the anticoagulant coating of the syringe/straw that the insect leaves behind in my epiderm when it's done extracting hemoglobin from me, and B) If I was not supremely angered by the fact that my blood will end up fertilizing hundreds of thousands of effing larvaes which will hatch and grow up to come and haunt me later in the season. It is simply maddening to cope with the thought that billions of them are somehow related to me in some more or less distant way.

But these insects are playing a role in the ecosystem. Their existence and succesful adaptation to a worldwide variety of climates is testament to their role in the overall scheme of things. I don't think synthetizing poisonous molecules is a solution, far from it.

So, God bless these researchers and their pursuit of a system to fend-off the annoyance while striving to find something, well... intelligent to deal with this problem.

There was an article somewhere I read recently about grapefruit extracts being really good at actually killing mosquitos, but this is still in research stage.

The chemical that you're referring to is called nootkatone. I saw it in an NPR article a while ago. It's not very harmful to humans. It binds to octopamine receptors in the mosquito, causing it to release an adrenaline-like chemical, shiver out of control, and die.

A couple of weeks ago in the woods at my place in Upstate NY I was walking around putting up some posted signs and throwing mosquito dunks (free from the town) in the many large pools of standing water spotted around the woods on the property. The mosquitos were like smoke in some areas. I had forgotten to spray any deet before setting off and brushed like 20 squiters off my arms and luckily had one of those pocket size Repel100 sprays in my pack which is almost 100% deet. Sprayed that on my arms and the back on my neck and ears and after that the little buggers just would bounce off my arms while walking through the thicker swarms. So at least in Saratoga County the mosquitos still don't like deet.